Created by M.L., OST, on 19.03.2025
Monitoring, and regular inspection of PV power plants is fundamental to ensure optimal electricity production. There exist many reports on best practices for operation and maintenance, such as [1–7], for example. Hereafter, we want to set a special focus on the implementation of such methods in alpine regions, highlighting additional challenges or benefits in this specific environment [2,8,9].
As a general note, a major challenge related to alpine PV plants is their often remote location, making on-site intervention time-consuming. The access with vehicles can be difficult, as well as highly dependent on the weather and is often impossible in winter. The severe weather conditions (snow load and drift, wind gusts, freezing temperatures, high irradiation; presented in more details here) represent a further challenge, requiring proper planning and increased robustness of the hardware (modules and mounting structure, for example), as well as regular inspection and monitoring. Since many of these phenomena very greatly with location, on-site measurements are essential to assess the quality of the building site and the local conditions.
The present article provides a general overview of measurement methods. More in-depth information is provided in specific articles to selected methods, linked here in the corresponding paragraphs. Moreover, further articles discuss the specific issues linked to off-grid installations, such as pilot test sites without existing grid connection, and advanced laboratory testing sequences developed specifically for extreme climate conditions.
Monitoring and data evaluation
Continuous real-time monitoring of the PV production, in order to detect power losses and track the production over the years.
Output monitoring
Real-time monitoring and logging of the inverter’s input and output values, including power, voltage, current.
Weather station
Real-time monitoring and logging of weather data, such as irradiance (global, direct, in-plane), albedo, ambient temperature, module temperature, wind speed, precipitation, relative humidity, air pressure, snow depth and cloud cover. Adding a webcam for remote visual inspection of the local conditions and the PV plant provides further valuable information.
Regular maintenance and measurement
Recommended work and measurements to complement the monitoring of the installation, maintain it and preemptively detect potential issues, minimizing the losses and risks of failures. Ideally, these tasks are performed in a single trip, reducing costs, but requiring all conditions to be met (access, irradiation, wind).
Visual inspection
Visual inspection of the PV plant. A rough overview can be gained remotely via webcams. However, a detailed inspection requires on-site human intervention. In some cases, a drone can be used for faster inspection.
I-V curve measurement
Measurement of the variation of current and voltage from the open-circuit to short-circuit condition by applying a variable load.
Isolation measurement
Measurement of the electrical resistance between the connectors and the earth (leakage current), as well as the continuity of the protective conductors.
Illuminated Thermography (IR)
Heat generation in the PV modules is detected using an infrared (IR) camera. The later can be hand-held, or mounted on a drone, allowing for fast measurements of large areas.
Cleaning of the installation
For practical reasons, the need for cleaning should be avoided. This is mainly achieved through steep inclination angles of the PV modules.
Troubleshooting
Due to their higher costs, the following methods are recommended only for failure diagnostics in case that the above methods did not success to identify the problem. Good overviews are presented in [5,10,11].
Electroluminescence (EL)
DC current is applied to the PV modules, which causes the cells to emit light, which is detected by a charged silicon camera. Regions with high signal are intact, whereas damaged areas will remain dark, allowing for defect localization.
Photoluminescence (PL)
Light emission from cells is measured, like for EL, but using light (instead of current) as excitation source. Lock-in amplification is used to filter out the sunlight, modulating the signal with a high power LED array [5,12]. As for EL, regions with high signal are intact, whereas damaged areas will remain dark, allowing for defect localization.
UV Fluorenscence (UV-F)
UV-F detects the luminophores generated when EVA degrades under UV radiation. Oxygen diffusing into the EVA reacts with the luminophores and deactivates them (photobleaching). Therefore, moisture ingress and cell cracks are visible as darker regions in the fluorescence image.
Individual measurement of PV-modules in a mobile laboratory
Detailed measurements of individual PV modules, typically in a mobile laboratory.
References
- Woyte A, Richter M, Moser D, Reich N, Green M, Mau S, et al. Analytical monitoring of grid-connected photovoltaic systems: good practices for monitoring and performance analysis. International Energy Agency (IEA); 2014. https://doi.org/10.2314/GBV:856977039.
- Jahn U, Herteleer B, Tjengdrawira C, Tsanakas I, Richter M, Dickeson G, et al. Guidelines for Operation and Maintenance of Photovoltaic Power Plants in Different Climates. International Energy Agency (IEA); 2022.
- Swissolar. Betrieb einer Photovoltaikanlage n.d. https://www.swissolar.ch/de/wissen/anlagenbetrieb (accessed November 18, 2024).
- Solar Best Practices. Guidelines – Solar Best Practices n.d. https://solarbestpractices.com/guidelines (accessed November 18, 2024).
- Hermann W, Eder G, Farnung B, Friesen G, Köntges M, Kubicek B, et al. Qualification of Photovoltaic (PV) Power Plants using Mobile Test Equipment. International Energy Agency (IEA); 2021.
- Electrosuisse. Photovoltaik(PV)-Systeme – Anforderungen an Prüfung, Dokumentation und Instandhaltung Teil 2: Netzgekoppelte Systeme Instandhaltung von PV-Systemen 2020.
- Electrosuisse. Betriebsverhalten von Photovoltaik-Systemen – Teil 1: Überwachung 2021.
- Nash A, Pike C, Seifert R. A Solar Design Manual for Alaska 2022. https://www.uaf.edu/ces/publications/database/energy/solar-energy-manual.php (accessed November 21, 2024).
- Koehl M, Heck M, Wiesmeier S. Categorization of weathering stresses for photovoltaic modules. Energy Sci Eng 2018;6:93–111. https://doi.org/10.1002/ese3.189.
- Rahman MM, Khan I, Alameh K. Potential measurement techniques for photovoltaic module failure diagnosis: A review. Renew Sustain Energy Rev 2021;151:111532. https://doi.org/10.1016/j.rser.2021.111532.
- Mühleisen W, Hirschl C, Brantegger G, Neumaier L, Spielberger M, Sonnleitner H, et al. Scientific and economic comparison of outdoor characterisation methods for photovoltaic power plants. Renew Energy 2019;134:321–9. https://doi.org/10.1016/j.renene.2018.11.044.
- Bhoopathy R, Kunz O, Juhl M, Trupke T, Hameiri Z. Outdoor photoluminescence imaging of photovoltaic modules with sunlight excitation. Prog Photovolt Res Appl 2018;26:69–73. https://doi.org/10.1002/pip.2946.
